This invention relates to a keyboard of a portable terminal which is used in dark environments such as the night outdoors.
FIG. 1 shows a portable terminal. The terminal includes a display panel 1 which can be read in the dark owing to the adoption of light emitting display elements or to an illuminating device provided for the case of non-luminant display elements such as liquid crystal elements, and an input panel 2 having operation keys, with the result of each operation appearing on the display panel. However, in order for the above-mentioned conventional panel design to have a luminous input panel, it would be necessary to provide illumination for the wide input panel area, and adding such an illumination device to the portable apparatus is difficult because of a resulting excessive weight and increased manufacturing cost.
A keyboard is known which is made of silicone rubber, however it does not have a luminant property and therefore the operator needs an external light source such a flashlight to recognize each key. Luminant pigments have been known, however, silicone rubber mixed with pigment spoils the working life of rubber in the stressed portion due to frequent operations or creates a disparity in its resilience.
FIG. 2 shows a key mat fitting structure for a conventional portable data terminal. A terminal unit 3 includes a key mat 4 made of a resin or paper sheet, on which key names are labeled. Key functions can be altered by a program stored in the terminal unit, and any key 2 can be given variable roles depending on the purpose of the terminal unit, and therefore the key mat 4 with the label of key names needs to be replaceable. Conventionally, a transparent sheet 5 has been used to settle the key mat 4 for the convenience of replacement. The settling sheet 5 is attached by inserting its four lugs 5a into sockets 3a formed in main frame.
FIG. 3 shows the foregoing structure in more detail. A key switch is turned "on" when a key 2 is pressed by a finger and an associated conductive contact 6 connects contacts 7 provided on a substrate 18. The key 2 has a name which is indicated by the label 11 printed on the key mat 10. The key mat 10 is settled in position by being placed between a main frame 9 and a transparent settling sheet 12 which is fitted as shown in FIG. 2.
However, the foregoing conventional key mat fitting structure compels the user to remove the settling sheet 12 at each replacement of the key mat 10, and it is unsuitable for applications which require frequent key mat replacements. The data terminal is occasionally used in the outdoors, and a key mat fitting structure which allows much easier replacement has been desired.